Industrial systems often times utilize fluid power systems to perform work, such as, to run hydraulic motors or to extend and retract cylinders in various manufacturing or production environments, for example. These fluid power systems include fluid pumps that are used to pressurize fluid, proportionate to a resistive load, such as hydraulic fluid, in the system. To pressurize the fluid, the pumps have rotating components that gradually wear over time and may eventually fail if the wear is left unchecked.
Failure of the pump can have catastrophic consequences. For example, if a pump abruptly fails, substantial debris can be introduced into the system causing damage to downstream components. In addition, catastrophic failures can result in substantial disruption of the manufacturing process. In view of the consequences of pump failure, it is desirable to perform periodic preventive maintenance of fluid power systems. During preventive maintenance, mechanics can replace worn pumps before they fail catastrophically, thus avoiding damage to other components or a major disruption in production.
One problem, however, is how to objectively schedule preventive maintenance. Generally, preventive maintenance schedules are developed from past experience and are subjective. Because pump wear cannot be easily monitored during operation, failures may not be easily predicted. In this regard, fluid pumps, and specifically piston pumps and piston motors, have an external case drain from which fluid leaks during operation based on designed leakage rates to provide hydrostatic balance of the pistons. This is accomplished by an orifice from the front of the piston (pressure side) to the balancing shoe, which has an area equal to the front or pressure side of the pistons. Fluid leakage from the case drain may be due to increased leakage within the pump around and between various components and seals in the pump. As any one or more of the components wears, the fluid exiting the case drain may increase. By sensing the flow of fluid through a case drain, an estimate of the remaining pump life may be made. In situations where the fluid exiting the case drain reaches a predetermined volume, preventive maintenance may be scheduled.
Prior art devices for measuring leakage from a case drain, however, are generally complicated in design and may be costly. One known device is disclosed in U.S. Pat. No. 5,563,351. However, the disclosed device is a complicated venturi design which requires sophisticated analysis techniques and may be difficult to calibrate. Furthermore, the disclosed design fails to provide any measurement of other parameters of the fluid power system at the case drain. Rather, other parameters, for example, temperature and pressure, are measured at the pump, which requires additional wiring and connectivity to the device. For this reason, such measurements are costly or may not be taken at all. In view of this deficiency, the information needed to predict an impending pump failure may be missing.
It would be desirable, accordingly, to provide devices that address these and other problems associated with conventional devices designed for such purpose.